A high voltage machine needs cooling to work properly. The rotor of the machine is generally cooled by means of axially mounted fans, which push air into both ends of the rotor, which air thereafter is released from the machine through radial air ducts in the stator of the machine. For a very high voltage machine the stator needs liquid cooling to work properly. It is however difficult to provide liquid cooling for a stator of a machine and still maintain good performance.
Air and liquid cooled high voltage machines are known in the literature e.g. U.S. Pat. No. 2,217,430 disclose a water cooled stator for a dynamo electric machine where the cooling devices are placed in the air ducts transporting cooling air from the rotor through the stator.
WO9745915 disclose a liquid cooled stator where the cooling fluid is arranged to circulate in the stator teeth.